Glow discharge tube and circuit therefor



y 1956 c. H. TOSSWILL GLOW DISCHARGE TUBE AND CIRCUIT THEREFOR Filed April 11 1951 m T N E V m CHRISTOPHER HALY TOSSWILL BYZ %W AGENT United States Patent GLOW DISCHARGE TUBE AND CIRCUIT THEREFOR Christopher Haly Tosswill, Carshalton, England, assignor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application April 11, 1951, Serial No. 220,424 Claims priority, application Great Britain April 13, 1950 3 Claims. (Cl. 315-168) This invention relates to devices comprising a glow discharge tube which is equipped with an ignition electrode and a screen surrounding the anode, and wherein substantially the whole wall is covered with a visible layer of a metal having a melting point higher than 1400 C. Furthermore the invention relates to glow discharge tubes for such devices.

In a known device of the aforesaid type, both the ignition electrode and the screen surrounding the anode are arranged at a distance from the anode substantially corresponding to the mean free path of the electrons in the gas filling of the tube so as to prevent excessive disintegration of the anode. In these tubes an auxiliary discharge does not occur.

It is also known to obviate delay of ignition in glow discharge tubes comprising a wall coating of refractory metal by producing in the tube an auxiliary discharge in the Townsend area. This tube does not comprise a separate ignition electrode.

According to the present invention, in a device comprising a glow discharge tube which is equipped with an ignition electrode and a screen surrounding the anode and wherein the wall is substantially entirely coated with a visible layer consisting of metal having a melting point higher than 1400, the ignition electrode is located in the proximity of the cathode, the screen surrounding the anode being at such a potential and being so spaced relatively to the anode as to produce an auxiliary discharge of a few microamps between the anode and the screen. Owing to diifusion of ions from the auxiliary discharge to the area between the cathode and the ignition electrode and owing also to ionisation occurring in the tube due to photons radiated from the auxiliary discharge, it is achieved that the ignition electrode requires only a constant low ignition voltage and that this voltage is practically of the same value for all tubes of the same type. The anode operating voltage is also constant in these tubes and equal for all of them.

The screen surrounding the anode is preferably connected through a high ohmic resistor to the cathode of the glow discharge.

The spacing between the anode and the screen electrode is to 100 times the mean free path of the electrons in the gas filling of the tube.

In order that the invention may be readily carried into effect, an example will now be described in detail with reference to the accompanying drawing, in which Fig. 1 is a vertical section of an electrode system, part broken away, of a glow discharge tube for use in a device according to the invention,

Fig. 2 is a plan view of this electrode system,

Fig. 3 is a schematic drawing showing the tube in a typical circuit.

In the drawing, reference numeral 1 denotes the glass 2,745,988 Patented May 15, 1956 bottom of the discharge tube, the remaining part of the bulb wall being designated 2. A thin molybdenum plate 4 constituting the cathode is secured to three lead-through pins 3. The ignition electrode consists of a stiff bent wire 5 secured to two lead-through pins 6, the anode 7 being constituted by an extension of a lead-through pin. The anode is surrounded by a cylindrical electrode or screen 8 intimately engaging the bead concerned on the glass bottom. The cylindrical electrode 8 is connected through two strips 9 and 10 to the lead-through pins 11. To prevent the molybdenum wall coating (not shown) obtained by disintegration from the molybdenum cathode, from adversely attecting the insulation resistance of the ignition electrode, a mica disc 12 clamped by a nickel ring 13 is provided around the glass beads at the leadthrough pins 6. The tube is operated in the circuit shown in Fig. 3 with an anode voltage of approximately 200 volts relative to the cathode, and a resistor 14 of 2, megohms between the cathode 4 and the screen 8. In this event, the ignition voltage required at the ignition electrode 5 is approximately volts. The lead-through pins consist of chrome iron, and the electrodes, similarly to the cathode, are made from molybdenum, the diameter of the glass base measured in the interior of the tube being approximately 16 rnms. The tube is filled with a suitable ionizable gaseous medium.

What I claim is:

1. A glow-discharge tube comprising an envelope containing an ionizable gaseous medium, a coating of metal having a melting point exceeding 1490 C. substantially entirely covering the inner wall of the envelope, a cathode, an ignition electrode positioned in close proximity to the cathode, an anode, and a screen electrode surrounding the anode, said screen being spaced from said anode a distance equal to about 10 to times the mean-freepath of electrons in the gaseous medium whereby an auxiliary discharge of the order of several microamperes may be produced between the anode and the screen.

2. A circuit arrangement including a glow discharge tube comprising an envelope containing an ionizable gaseous medium, a coating of metal having a melting point exceeding 1400 C. substantially entirely covering the inner wall of the envelope, a cathode, an ignition electrode positioned in close proximity to the cathode, an anode, and a screen electrode surrounding the anode and spaced therefrom a distance equal to about 10 to 100 times the mean-free-path of electrons in the gaseous medium, means applying a positive potential to the anode relative to the cathode, a high ohmic resi tance connected between the screen and the cathode, whereby an auxiliary discharge of the order of several microamperes is produced between the screen and the anode, and means for applying a voltage to the ignition electrode to effect ignition of a discharge in the tube.

3. A circuit arrangement as set forth in claim 2 wherein the ohmic resistance is two megohms.

References Cited in the file of'this patent UNITED STATES PATENTS 2,035,784 B01 et a1 Mar. 31, 1936 2,129,314 Boumeester Sept. 6, 1938 2,129,357 Marden et al Sept. 6, 1938 2,404,413 Stutsman July 23, 1946 2,541,335 Carne Feb. 13, 1951 2,560,346 Holdaway July 10, 1951 2,577,352 Mulder et a1 Dec. 4,- 1951 2,584,758 Stutsman Feb. 5, 1952 

1. A GLOW-DISCHARGE TUBE COMPRISING AN ENVELOPE CONTAINING AN IONIZABLE GASEOUS MEDIUM, A COATING OF METAL HAVING A MELTING POINT EXCEEDING 1400* C. SUBSTANTIALLY ENTIRELY COVERING THE INNER WALL OF THE ENVELOPE, A CATHODE, AN IGNITION ELECTRODE POSITIONED IN CLOSE PROXIMITY TO THE CATHODE, AN ANODE, AND A SCREEN ELECTRODE SURROUNDING THE ANODE, SAID SCREEN BEING SPACED FROM SAID ANODE A DISTANCE EQUAL TO ABOUT 10 TO 100 TIMES THE MEAN-FREEPATH OF ELECTRONS IN THE GASEOUS MEDIUM WHEREBY AN AUXILIARY DISCHARGE OF THE ORDER OF SEVERAL MICROAMPERES MAY BE PRODUCED BETWEEN THE ANODE AND THE SCREEN. 